SLUDGE VOLUME INDEX SETTLEABILITY MEASURES - EFFECT OF SOLIDS CHARACTERISTICS AND TEST PARAMETERS

Sludge volume index (SVI) type activated-sludge settleability measures are used in the design and control of secondary settling tanks. Consi derable confusion exists as to the best parameter and experimental tec hnique to use. The common settleability measures (SVI, diluted sludge volume index, stirred specific volume index [SSVI], and SSVI at 3.5 g/ L) are outlined. This discussion is used as the basis for commenting o n the validity of these measures and their relation to zone settling v elocity measurements. A simple mechanistic model is used to evaluate t he effects of solids characteristics and test parameters on SVI-type i ndices. Solids settleability and compactability, settling column heigh t, and solids concentration in the test have an interactive effect on the measured SVI. The applied model explains many of the artifacts ass ociated with SVI and questions the validity of correlations for zone s ettling parameters based on SVI-type measurements.